Cooling fan control apparatus and cooling fan control method for radiator

ABSTRACT

An electronic control unit is used in an internal combustion engine capable of using a fuel in which ethanol is mixed with gasoline, the cooling fan control apparatus that controls the drive of an electric cooling fan provided in a radiator of the internal combustion engine. This controller performs the drive of the cooling fan after the internal combustion engine is stopped, when an alcohol concentration of the fuel is higher than a predetermined concentration, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a cooling fan control apparatus and a cooling fan control method for a radiator that are used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, to control an electric cooling fan provided in the radiator of the internal combustion engine.

2. Description of Related Art

For example, there are internal combustion engines capable of using a fuel in which gasoline is mixed with ethanol (see, for example, Japanese Patent Application Publication No. 2010-1752 (JP 2010-1752 A)). A vehicle is provided with a radiator for cooling the engine cooling water. The cooling water flowing in the radiator is cooled by the heat exchange performed between the cooling water and the air passing through the radiator when the vehicle runs, that is, running air which is air flow caused by travel of the vehicle.

The vehicle is also provided with a cooling fan for blowing the air onto the radiator. When a sufficient amount of running air which is air flow caused by travel of the vehicle cannot be obtained, for example, when the vehicle stops or runs at a low speed, the cooling fan is driven to ensure the flow rate of the air passing through the radiator.

However, where the vehicle stops in a state in which the engine temperature is high, the cooling water is not cooled because no running air which is air flow caused by travel of the vehicle passes through the radiator. Therefore, the engine is maintained at a high temperature. Where a fuel supply system such as a delivery pipe or an injector is heated by the heat transmitted or radiated from the high-temperature engine, evaporation, in particular, of ethanol, which has a boiling point lower than that of gasoline, is enhanced and vapor is generated in the liquid fuel. As a result, when the engine is restarted, the fuel cannot be injected from the injector in an amount matching the engine operation state, the so-called vapor lock phenomenon occurs, and engine operation can become unstable.

Where the cooling fan is operated at all times when the engine is stopped, the instability of engine operation when the engine is restarted can be inhibited. However, in this case the cooling fan is operated even when the vapor is not generated and the battery power is unnecessarily consumed to drive the cooling fan.

The above-described case is not limited to the internal combustion engines capable of using a fuel in which ethanol is mixed with gasoline having a boiling point higher than that of ethanol, and is generally common to the internal combustion engines capable of using fuels in which other alcohol fuels are mixed with gasoline.

SUMMARY OF THE INVENTION

The invention provides a cooling fan control apparatus and a cooling fan control method for a radiator that can inhibit battery power consumption associated with the drive of the cooling fan, while inhibiting the unstable operation of the engine when the engine is restarted.

The cooling fan control apparatus for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, the cooling fan control apparatus comprising: a controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when an alcohol concentration of the fuel is higher than a predetermined concentration, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration.

Therefore, the battery power consumption associated with the drive of the cooling fan can be inhibited, while inhibiting the instability of engine operation when the engine is restarted.

In the cooling fan control apparatus for a radiator according to the first aspect of the invention, the predetermined concentration may be an alcohol concentration of the fuel when a boiling point of the fuel that changes according to the alcohol concentration of the fuel is at a maximum value attainable by a temperature of the fuel after the internal combustion engine is stopped.

In the cooling fan control apparatus for a radiator according to the first aspect of the invention, the controller that prohibits the drive of the cooling fan after the internal combustion engine is stopped, when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration.

In the cooling fan control apparatus for a radiator according to the first aspect of the invention, the controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when an evaporation amount of the fuel inside a fuel tank after a supply of the fuel to the fuel tank is performed is less than a predetermined amount, the alcohol concentration of the fuel is taken to be higher than the predetermined concentration, and that restricts the drive of the cooling fan after the to internal combustion engine is stopped, when the evaporation amount of the fuel inside the fuel tank after the supply is performed is equal to or greater than the predetermined amount, the alcohol concentration of the fuel is taken to be equal to or lower than the predetermined concentration.

Therefore, the alcohol concentration of the fuel stored in the fuel tank can be indirectly determined on the basis of the evaporation amount of the fuel inside the same fuel tank after the fuel is fed into the fuel tank.

In the cooling fan control apparatus for a radiator according to the first aspect of the invention, the internal combustion engine is provided with an intake passage for introducing intake air into the internal combustion engine, and an evaporated fuel processing device that introduces an evaporated fuel produced by evaporation of the fuel inside the fuel tank, into the intake passage, the controller that calculates a purge amount integral value which is an integral value of an amount of the evaporated fuel introduced into the intake passage after the supply of the fuel to the fuel tank is performed, that performs the drive of the cooling fan after the internal combustion engine is stopped, when the purge amount integral value is less than a predetermined value, the alcohol concentration of the fuel is taken to be higher than the predetermined concentration, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the purge amount integral value is equal to or higher than the predetermined value, the alcohol concentration of the fuel is taken to be equal to or lower than the predetermined concentration.

The cooling fan control apparatus for a radiator according to the first aspect of the invention may include an estimation device that estimates an alcohol concentration of the fuel, wherein when the alcohol concentration of the fuel estimated by the estimation device is equal to or lower than the predetermined concentration, the drive of the cooling fan after the internal combustion engine is stopped is restricted. In this case, the alcohol concentration of the fuel can be determined even if the evaporation amount of the fuel inside the fuel tank after the feed has been performed is not determined. Therefore, the increase in the computation load associated with the calculation of the evaporation amount can be avoided.

In the cooling fan control apparatus for a radiator according to the first aspect of the invention, the controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration, regardless of the evaporation amount of the fuel inside the fuel tank after the supply of the fuel to the fuel tank.

The cooling fan control apparatus for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, the cooling fan control apparatus comprising: a controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when an evaporation amount of the alcohol in the fuel inside a fuel tank after a supply of the fuel into the fuel tank is performed is less than a predetermined amount, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the evaporation amount of the alcohol after the supply is performed is equal to or greater than the predetermined amount.

In accordance with the above-described configuration, whether or not to drive the cooling fan is determined on the basis of the evaporation amount of the alcohol of the fuel inside the fuel tank. Therefore, the battery power consumption associated with the drive of the cooling fan can be inhibited, while inhibiting the instability of engine operation when the engine is restarted.

The cooling fan control apparatus for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, the cooling fan control apparatus comprising: a controller that performs the drive of the cooling fan after the internal combustion engine is stopped, before a predetermined period elapses from a supply of the fuel to a fuel tank, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, after the predetermined period has elapsed from the supply.

A cooling fan control method for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, comprising: driving the cooling fan after the internal combustion engine is stopped when an alcohol concentration of the fuel is higher than a predetermined concentration; and restricting the drive of the cooling fan after the internal combustion engine is stopped when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration.

A cooling fan control method for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, comprising: driving the cooling fan after the internal combustion engine is stopped when an evaporation amount of the alcohol in the fuel inside a fuel tank after a supply of the fuel into the fuel tank is performed is less than a predetermined amount; and restricting the drive of the cooling fan after the internal combustion engine is stopped when the evaporation amount of the alcohol after the supply is performed is equal to or greater than the predetermined amount.

A cooling fan control method for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, comprising: driving the cooling fan after the internal combustion engine is stopped, before a predetermined period elapses from a supply of the fuel to a fuel tank; and restricting the drive of the cooling fan after the internal combustion engine is stopped, after the predetermined period has elapsed from the supply.

In accordance with the above-described configuration, whether or not to drive the cooling fan is determined on the basis of the period that has elapsed since the feed of the fuel to the fuel tank has been performed. Therefore, the battery power consumption associated with the drive of the cooling fan can be inhibited, while inhibiting the instability of engine operation when the engine is restarted.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic configuration diagram relating to a cooling fan control apparatus for a radiator according to one embodiment of the invention and illustrating the schematic configuration of the internal combustion engine of the vehicle using the apparatus;

FIG. 2 is a graph illustrating the relationship between the ethanol concentration of a fuel and the boiling point of the fuel;

FIG. 3 is a timing chart illustrating changes in the ethanol concentration of the fuel and also in the boiling point of the fuel;

FIG. 4 is a flowchart illustrating the processing sequence of the cooling fan drive control performed when the internal combustion engine is stopped in the configuration of the same embodiment;

FIG. 5 is a flowchart illustrating the processing sequence for setting a drive prohibition flag in the same embodiment;

FIG. 6 is a flowchart illustrating the processing sequence for setting a drive prohibition flag in another embodiment; and

FIG. 7 is a flowchart illustrating the processing sequence for setting a drive prohibition flag in another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment in which the cooling fan control apparatus for a radiator in accordance with the invention is specifically implemented will be described below with reference to FIGS. 1 to 5. FIG. 1 illustrates the schematic configuration of an internal combustion engine for a vehicle to which the invention is applied (referred to hereinbelow as internal combustion engine 1 or engine). The vehicle is a hybrid car provided with the internal combustion engine 1 and an electric motor as drive sources. The internal combustion engine 1 is an engine of a port injection system capable of using a mixed fuel of gasoline and ethanol, which has a boiling point lower than that of the gasoline, as a fuel.

As shown in FIG. 1, the internal combustion engine 1 is provided with an intake passage 2 for introducing the intake air into a combustion chamber 11 and an exhaust passage 3 for discharging the exhaust air from the combustion chamber 11. An air cleaner 21, a throttle valve 22, and a surge tank 24 are provided in the intake passage 2 in the order of description from the intake upstream side. A throttle motor 23 that opening-closing drives the throttle valve 22 is also provided.

The fuel located in the fuel tank 41 is sucked in by the fuel pump 42, pumped through a fuel supply passage 43, and supplied to an injector 44. The fuel is injected from the injector 44 provided in the intake port toward the combustion chamber 11. A fuel supply system 4 is constituted by the fuel tank 41, the fuel pump 42, the fuel supply passage 43, and the injector 44.

The internal combustion engine 1 is also provided with a sparkplug 12 that ignites the gas mixture of the intake air and the fuel injected from the injector 44. A cooling apparatus 5 is provided in the vehicle for cooling the internal combustion engine 1. The cooling apparatus 5 cools the internal combustion engine 1 by pumping the cooling water discharged from a water pump 52 to a water jacket 53 formed inside a cylinder block and a cylinder head. The cooling water discharged from the water jacket 53 is introduced into the radiator 54 via a cooling water passage 51. When the cooling water circulates inside the radiator 54, the cooling water is cooled by the heat exchange performed between the cooling water and the running air which is air flow caused by travel of the vehicle passing through the radiator 54. The vehicle is also provided with an electric cooling fan 55 that blows air onto the radiator 54.

The internal combustion engine 1 is provided with an evaporated fuel processing device 6 that introduces into the intake passage 2 and processes the evaporated fuel produced by the evaporation of the fuel inside the fuel tank 41. The evaporated fuel processing device 6 is provided with a canister 61 having an adsorbing material that adsorbs fuel components. The canister 61 is connected via a vapor passage 62 to the fuel tank 41. A release passage 64 is connected to the canister 61. As a result, the fuel components contained in the air that is introduced from the fuel tank 41 into the canister 61 through the vapor passage 62 are adsorbed in the canister 61 and the air is purified. The purified air is released to the atmosphere through the release passage 64.

The canister 61 is also provided with a purge passage 63 communicating with the intake passage 2. An electric control valve 65 is provided in the intermediate section of the purge passage 63. In the evaporated fuel processing device 6 of such a configuration, when the control valve 65 is open, the air located inside the canister 61 is sucked out into the intake passage 2 through the purge passage 63 by the negative pressure in the intake passage 2. In this case, the introduction of new air from the release passage 64 results in the desorption of the fuel components adsorbed in the canister 61, the new air is mixed with those fuel components to form a purge gas, and this purge gas is introduced into the intake passage 2. Thus, the execution of the so-called purge control by which the fuel components adsorbed in the canister 61 are desorbed and the purge gas is introduced into the intake passage 2 and subjected to combustion restores the capacity of the canister 61 to adsorb the fuel components.

Various types of control of the internal combustion engine 1, opening degree control of the control valve 65, and drive control of the cooling fan 55 are performed by an electronic control unit 9. The internal combustion engine 1 is provided with various sensors that detect the operating state of the engine, for example, an engine speed sensor 91 that detects an engine speed NE, an intake amount sensor 92 that detects an intake amount GA, a throttle opening degree sensor 93 that detects a throttle opening degree TA, a water temperature sensor 94 that detects a cooling water temperature THW, and an air-fuel ratio sensor 95 that detects an air-fuel ratio AF of the exhaust gas. Sensors of other types, such as a liquid level sensor 96 that detects a liquid level L of the fuel in the fuel tank 41 and an IG switch 97 are also provided. Those sensors are electrically connected to the electronic control unit 9.

Various sensors that detect the vehicle running state, such as an accelerator depression amount ACCP, a brake depression amount B, and a vehicle speed V are also electrically connected to the electronic control unit 9. The electronic control unit 9 is constituted by a central processing unit (CPU) that implements computational processing relating the various types of control, a read only memory (ROM) where programs and data for the aforementioned various types of control are stored, and a random access memory (RAM) where the results of the computational processing are temporarily stored. The electronic control unit 9 reads the detection signals for the above-mentioned sensors, executes various types of computational processing, and integrally controls the vehicle (internal combustion engine 1, control valve 65, and cooling fan 55) on the basis for the processing results.

More specifically, where the IG switch 97 is ON, the electronic control unit 9 drives the start motor, performs cranking, and starts the fuel injection control and ignition control, thereby starting the engine. Where the IG switch 97 is OFF, the electronic control unit stops the ignition of fuel from the injector 44 and stops the operation of the engine.

The electronic control unit 9 performs the air-fuel ratio feedback control by which the fuel injection amount is controlled so as to obtain the stoichiometric air-fuel ratio. The electronic control unit 9 also performs the purge control of regulating the amount of the purge gas introduced into the intake passage 2 by adjusting the opening degree of the control vale 65.

The relationship between the air-fuel ratio feedback control and purge control will be described below. The air-fuel ratio feedback control is performed by feedback controlling the fuel injection amount on the basis of the output of the air-fuel ratio sensor 95, basically so as to maintain the air-fuel ratio close to the stoichiometric air-fuel ratio.

However, when the purge gas including the fuel components is introduced into the intake passage 2 by means of the purge control, the fuel contained in the purge gas is supplied to the combustion chamber 11 in addition to the fuel injected from the injector 44, thereby shifting the air-fuel ratio. Accordingly, in the air-fuel ratio feedback control, the reduction correction of the fuel injection amount is performed to reduce the amount of fuel injected from the injector 44 by the amount of fuel contained in the purge gas as long as the purge gas is introduced by the purge control. The amount of fuel contained in the purge gas (referred to hereinbelow as purge amount PG) is calculated for each predetermined time interval by the electronic control unit 9 on the basis of the purge gas flow rate and the purge concentration D that is learned by a conventional procedure when the engine operates. The above-mentioned reduction correction is performed on the basis of the amount of fuel that has thus been calculated. Incidentally, in the present embodiment, the purge amount PG is calculated by the following Eq. (1).

PG=GA×R×D  (1)

In this case, the flow rate of the purge gas is calculated by multiplying the intake amount GA by the purge ratio R, which is the ratio of the purge gas contained in the intake air, and then the purge amount PG is calculated by multiplying the obtained product by the purge concentration D.

Further, the electronic control unit 9 also performs the drive control of the cooling fan 55 such that the flow rate of air passing through the radiator 54 is ensured when the sufficient amount of running air which is air flow caused by travel of the vehicle cannot be obtained, for example, when the vehicle is stopped or travels at a low speed.

However, as mentioned hereinabove, where the vehicle stops in a state in which the engine temperature is high, no running air which is air flow caused by travel of the vehicle passes through the radiator 54 and the cooling water cannot be cooled. As a result, the engine is maintained at a high temperature. Where the fuel supply system 4, for example, the fuel supply passage 43 or injector 44, is heated by the heat transferred or radiated from the high-temperature engine, the evaporation, in particular, of ethanol, which has a boiling point lower than that of gasoline, is enhanced and vapor is generated in the liquid fuel. As a result, when the internal combustion engine 1 is restarted, the fuel cannot be injected from the injector 44 in an amount matching the engine operating state, the so-called vapor lock phenomenon occurs, and engine operation can become unstable.

Accordingly, in the present embodiment, the occurrence of the to above-described inconveniences is inhibited by performing the below-described drive control of the cooling fan. Thus, after the feed in which the fuel is supplied to the fuel tank 41 has been performed, the amount of evaporated fuel introduced into the intake passage 2, that is, the purge amount PG, is calculated and the integral value (referred to hereinbelow as purge amount integral value PGS) of the purge amount PG is calculated. Then, where the purge amount integral value PGS is less than a predetermined value PGSth, the cooling fan 55 is driven after the engine stop, but where the purge amount integral value PGS is equal to or higher than the predetermined amount PGSth, the drive of the cooling fan 55 after the engine stop is prohibited.

The reason for determining whether or not to drive the cooling fan 55 when the engine is stopped according to the purge amount integral value PGS after the feed has been performed will be explained below. FIG. 2 shows the relationship between the ethanol concentration E of the fuel and the boiling point Tbp of the fuel.

The boiling point (about 78° C.) of the ethanol is lower than the boiling point of gasoline (in the present embodiment, 120° C.). Thus, as shown in FIG. 2, when the ethanol concentration E of the fuel is 0%, the boiling point Tbp of the fuel is 120° C. Within a range of the ethanol concentration E of the fuel from 0% to about 20%, the boiling point Tbp of the fuel decreases with the increase of the ethanol concentration E of the fuel, and when the ethanol concentration E of the fuel is 20%, the boiling point Tbp of the fuel becomes about 111.5° C. Incidentally, within a range in which the ethanol concentration E of the fuel is higher than 20%, the boiling point Tbp of the fuel increases with the increase in ethanol concentration E of the fuel. In FIG. 2, the maximum temperature T_(max) (in the present embodiment, 112° C.) attainable by the temperature of the fuel in the fuel supply system 4 after the engine stop is shown by a dot-dash line.

Thus, when the ethanol concentration E of the fuel is equal to or higher than the predetermined concentration Eth within the range of ethanol concentration E of the fuel shown in FIG. 2 (0%≦E≦20%), the boiling point Tbp of the fuel is below the abovementioned maximum attainable temperature Tmax. In this case, because a state can be assumed in which the temperature of the fuel in the fuel supply system 4 exceeds the boiling point Tbp of the fuel after the engine stop, the ethanol contained in the fuel can be evaporated. The lower is the boiling point of the fuel, the easier it is for the temperature of the fuel in the fuel supply system, for example in the injector, to surpass the boiling point of the fuel and the easier it is for the evaporation of the alcohol contained in the fuel to advance and for the vapor to be generated in the liquid fuel.

Meanwhile, when the ethanol concentration E of the fuel is lower than the abovementioned predetermined concentration Eth, the boiling point Tbp of the fuel exceeds the maximum attainable temperature Tmax. In this case, since the temperature of the fuel in the fuel supply system after the engine stop cannot rise above the boiling point Tbp of the fuel, the ethanol contained in the fuel is not evaporated.

Therefore, where the fuel temperature starts rising in the course of engine operation after the ethanol concentration E of the fuel inside the fuel tank 41 has been made, for example, 20% by feeding the fuel into the fuel tank 41, the boiling point Tbp of the fuel and the ethanol concentration E of the fuel change, for example, as shown in FIG. 3. Thus, as shown in FIG. 3, where the elapsed time t of engine operation after the aforementioned feed becomes the first predetermined time t1, the ethanol concentration E of the fuel initially decreases gradually because the ethanol, which has a low boiling point, is the first to start evaporating. Then, following this decrease in ethanol concentration, the boiling point Tbp of the fuel rises gradually from 111.5° C. Where the second predetermined time t2 thereafter elapses, the ethanol concentration E of the fuel becomes equal to or lower than the predetermined concentration Eth, and the boiling point Tbp of the fuel becomes equal to or higher than the maximum attainable temperature Tmax. In FIG. 3, the ethanol concentration E of the fuel is shown by a dot-dash line and the boiling point Tbp of the fuel is shown by a solid line.

There is a correlation between the ethanol concentration E of the fuel and the fuel amount evaporated from the fuel stored in the fuel tank 41 after the feed of the fuel into the fuel tank 41 has been performed. Further, as described hereinabove, there is also a correlation between the amount of fuel evaporated from the fuel stored in the fuel tank 41 and the integral value of the purge amount PG after the feed has been performed (referred to hereinbelow as purge amount integral value PGS). Therefore, in the present embodiment, whether or not to drive the cooling fan 55 when the engine is stopped is determined according to the purge amount integral value PGS.

The specific processing procedure of the cooling fan drive control when the engine is stopped will be explained below with reference to FIG. 4. The series of processing steps shown in FIG. 4 is executed repeatedly with a predetermined period during electricity supply to the electronic control unit 9.

As shown in FIG. 4, in this series of processing steps, first, in step S1, it is determined whether or not an engine stop command has been outputted. In this case, it is determined whether or not the engine stop command has been outputted when the OFF operation for the IG switch 97 has been detected. When it is not determined that the engine stop command has been outputted (step S1: “NO”), the present timing is assumed not to be the timing for executing the cooling fan drive control and the series of processing steps is ended.

Meanwhile, where it is determined in step S1 that the engine stop command has been outputted (step S1: “YES”), the processing advances to step S2 and it is determined whether or not the drive prohibition flag F is “OFF”.

The setting processing procedure for the drive prohibition flag is explained hereinbelow with reference to FIG. 5. The series of processing steps shown in FIG. 5 is executed repeatedly with a predetermined period during engine operation. The drive prohibition flag F is initially set to “OFF”.

As shown in FIG. 5, in this series of processing steps, first, in step S11, it is determined whether or not the fuel has been fed immediately therebefore. In this case, it is determined that the fuel has not been fed immediately therebefore when the level L of the fuel inside the fuel tank 41 that is detected by the liquid level sensor 96 has not risen above a value detected in the preceding control period by an amount equal to or higher than a predetermined value. As a result, when it is determined that the fuel has been fed immediately therebefore (Step S11: “YES”), the processing advances to step S12, the increase in the ethanol concentration E of the fuel by the fuel feed is assumed to be possible, “0” is set as the purge amount integral value PGS, and the series of processing steps is ended. In this case, it is assumed that the cooling fan 55 should be driven when the engine is stopped and the drive prohibition flag F is left unchanged at “OFF”.

Meanwhile, when it is determined that the fuel has not been fed immediately therebefore (Step S11: “NO”), the processing advances to step S13, and the purge amount integral value PGS is updated. More specifically, the purge amount PG introduced into the intake passage 2 within the interval after the preceding control period to the present control period is calculated and the new purge amount integral value PGS is obtained by adding the calculated purge amount PG to the purge amount integral value PGS in the preceding control period.

Where the purge amount integral value PGS is thus updated, the processing then advances to step S14, and it is determined whether or not the purge amount integral value PGS that has been updated in step S13 is equal to or higher than a predetermined value PGSth. In this case, the predetermined value PGSth is set in advance by a test or modulation in the following manner. Thus, the predetermined value PGSth is set to the purge amount integral value PGS assumed when the ethanol concentration E for the fuel becomes the aforementioned predetermined concentration Eth due to advance in evaporation of ethanol from the state in which the fuel tank 41 is filled with the fuel with an ethanol concentration E of 20%.

When the purge amount integral value PGS is determined in step S14 to be equal to or higher than the abovementioned predetermined value PGSth (step S14: “YES”), it is assumed that the ethanol concentration E of the fuel is equal to or lower than the predetermined concentration Eth because a large amount of ethanol has evaporated from the fuel inside the fuel tank 41, the processing then advances to step S15, the drive prohibition flag F is set to “ON”, and this series of processing steps is ended.

Meanwhile, when the purge amount integral value PGS is determined in step S14 to be less than the predetermined value PGSth (S14: “NO”), it is assumed that the ethanol has not significantly evaporated from the fuel inside the fuel tank 41 and the ethanol concentration E of the fuel is higher than the predetermined concentration Eth, and this series of processing steps is ended. In this case, it is assumed that the cooling fan 55 should be driven when the engine is stopped and the drive prohibition flag F is left unchanged at “OFF”.

As shown in the aforementioned FIG. 4, when the drive prohibition flag F is “OFF” in step S2, the processing then advances to step S3 and the cooling fan 55 is driven. The processing thereafter advances to step S5, and it is determined whether or not a drive stop condition for stopping the drive of the cooling fan 55 has been established. More specifically, it is determined whether or not the drive stop condition has been established in the case in which the elapsed time since the drive of the cooling fan 55 has been started has become a predetermined time period. In this case, when the drive stop condition has not been established (step S5: “NO”), the drive of the cooling fan 55 is continued and this series of processing steps is ended.

Meanwhile, where the drive stop condition has been determined in step S5 to be established (step S5: “YES”), the processing advances to step S6, the drive of the cooling fan 55 is stopped, and this series of processing steps is ended.

Further, when the drive prohibition flag F is “OFF” in step S2, the processing further advances to step S4, the drive of the cooling fan 55 is prohibited, and this series of processing steps is ended.

The operation of the present embodiment will be explained below. In the present embodiment, when a sufficient amount of running air which is air flow caused by travel of the vehicle cannot be obtained, for example, when the vehicle stops or runs at a low speed, the cooling fan 55 is driven to ensure the flow rate of the air passing through the radiator 54.

Further, the purge amount integral value PGS after the feed of fuel to the fuel tank 41 has been performed is calculated. When the purge amount integral value PGS is less than the predetermined value PGSth, it is possible that the ethanol concentration E of the fuel exceeds the predetermined concentration Eth and the temperature of the fuel in the fuel supply system 4 after the engine stop can rise above the boiling point Tbp of the fuel, it is assumed that the vapor is generated in the liquid fuel, and the cooling fan 55 is driven after the engine stop. As a result, the generation of vapor in the liquid fuel can be inhibited, and the occurrence of the vapor lock phenomenon in a subsequent engine restart and the impossibility of fuel injection caused by this phenomenon can be inhibited.

Meanwhile, when the purge amount integral value PGS is equal to or higher than the predetermined value PGSth, the ethanol concentration E of the fuel is equal to or lower than the predetermined concentration Eth, and even if the temperature of the fuel in the fuel supply system 4 after the engine stop is the maximum attainable temperature Tmax, it is assumed that the fuel temperature does not rise above the boiling point Tbp of the fuel and no vapor is generated in the liquid fuel, and the drive of the cooling fan 55 is prohibited. As a result, the unnecessary drive of the cooling fan 55 can be inhibited as long as no vapor is generated in the liquid fuel. Therefore, battery power consumption on the drive of the cooling fan 55 can be inhibited.

The electronic control unit 9 corresponds to the cooling fan control apparatus for a radiator in accordance with the invention. The following operation effects can be obtained with the cooling fan control apparatus for a radiator according to the above-described embodiment.

(1) The internal combustion engine 1 is provided with the evaporated fuel processing device 6 that introduces the evaporated fuel located inside the fuel tank 41 into the intake passage 2 and processes the introduced fuel. The electronic control unit 9 is used in the internal combustion engine 1 capable of using a fuel obtained by mixing ethanol and gasoline, which has a boiling point higher than that of ethanol, and controls the drive of the electric cooling fan 55 provided in the radiator 54 of the internal combustion engine 1. The electronic control unit 9 calculates the purge amount integral value PGS, which is the integral value of the evaporated fuel amount introduced into the intake passage 2 after the feed of the fuel into the fuel tank 41 has been performed. When the purge amount integral value PGS is less than the predetermined value PGSth, the electronic control unit 9 assumes that the ethanol concentration E of the fuel can be higher than the predetermined concentration Eth and drives the cooling fan 55 after the engine stop. Meanwhile, when the purge amount integral value PGS is equal to or higher than the predetermined value PGSth, the electronic control unit 9 assumes that the ethanol concentration E of the fuel is equal to or lower than the predetermined concentration Eth and prohibits the drive of the cooling fan 55 after the engine stop. With such a configuration the battery power consumption associated with the drive of the cooling fan 55 can be inhibited, while inhibiting the unstable operation of the engine when the engine is restarted.

The cooling fan control apparatus for a radiator in accordance with the invention is not limited to the configuration presented by way of example in the above-described embodiment, and this apparatus can be also implemented, for example, in the following modes obtained by appropriate modification thereof.

In the abovementioned embodiment and a variation example thereof, ethanol is presented as an example of the alcohol contained in the fuel, but the alcohol in accordance with the invention is not limited to ethanol, and the ethanol can be replaced with another alcohol, provided that the boiling temperature of this alcohol is lower than that of gasoline.

In the abovementioned embodiment, the amount of the evaporated fuel inside the fuel tank 41 after the fuel is fed is determined on the basis of the purge amount integral value PGS, but the invention is not limited to this feature. Thus, the amount of the evaporated fuel inside the fuel tank 41 after the fuel is fed, that is, the ethanol concentration E of the fuel, may be also determined on the basis of changes in the below-described parameters, instead of the purge amount integral value PGS or in addition to the purge amount integral value PGS. At least one of the external air temperature, engine operation retention period, and vehicle running distance can be used as the parameter.

With the above-described configuration, when the alcohol concentration of the fuel is higher than the predetermined concentration Eth, it is assumed that the temperature of the fuel in the fuel supply system after the engine stop rises above the boiling point of the fuel and vapors can be generated in the liquid fuel, and the cooling fan is driven. As a result, it is possible to inhibit the generation of vapors inside the liquid fuel by cooling the fuel. Therefore, the occurrence of the vapor lock phenomenon in a subsequent engine restart and the impossibility of fuel injection caused by this phenomenon can be inhibited.

Meanwhile when the alcohol concentration of the fuel is equal to or lower than the abovementioned predetermined concentration, even if the temperature of the fuel in the fuel supply system after the engine stop is the maximum attainable temperature, it is assumed that the boiling point of the fuel is not exceeded and no vapor occurs in the liquid fuel, and the drive of the cooling fan is restricted. As a result, the unnecessary drive of the cooling fan can be inhibited as long as no vapor is generated in the liquid fuel, and battery power consumption associated with the drive of the cooling fan can be inhibited. Therefore, battery power consumption associated with the drive of the cooling fan, while inhibiting the unstable operation of the engine when the engine is restarted.

Where the temperature of the fuel stored inside the fuel tank rises as the external air temperature rises or the engine continues operating, the alcohol with a low boiling point is the first to evaporate. Therefore, with the above-described configuration, when the evaporation amount of the fuel inside the fuel tank after the feed of the fuel to the fuel tank has been performed is less than the predetermined amount, it is assumed that the amount of alcohol evaporated from the fuel stored in the fuel tank is small and a large amount for the alcohol is contained in the fuel, and the alcohol concentration of the fuel can be considered to be higher that the abovementioned predetermined concentration.

Meanwhile, when the evaporation amount of the fuel inside the fuel tank after the feed of the fuel into the fuel tank has been performed is equal to or higher than the abovementioned predetermined amount, it is assumed that a large amount of alcohol has evaporated from the fuel stored in the fuel tank and the fuel does not contain a large amount of alcohol, and the alcohol concentration of the fuel can be considered to be equal to or lower than the predetermined concentration. Therefore, the alcohol concentration of the fuel stored in the fuel tank can be indirectly determined on the basis of the evaporation amount of the fuel inside the fuel tank after the feed of the fuel into fuel tank has been performed.

In the abovementioned embodiment and a variation example thereof, the ethanol concentration E of the fuel is determined from the evaporated fuel amount inside the fuel tank 41 after the fuel is supplied therein, but the ethanol concentration E of the fuel may be instead estimated as in the conventional configuration, for example, on the basis of the air-fuel ratio AF of the exhaust gas detected by the air-fuel ratio sensor 95. In this case, the air-fuel ratio sensor 95 and the electronic control unit 9 correspond to the estimation device in accordance with the invention. When the ethanol concentration of the fuel estimated by the estimation device is equal to or lower than the predetermined concentration, the drive of the cooling fan after the engine stop may be restricted regardless of the evaporation amount of the fuel inside the fuel tank after the feed of the fuel to into the fuel tank has been performed.

Instead of the abovementioned embodiment and the variation example thereof, it is possible to drive the cooling fan 55 after the engine stop before a predetermined period elapses (elapsed time T) since the feed of the fuel into the fuel tank 41 has been performed, and prohibit the drive of the cooling fan 55 after the engine stop after the predetermined period has elapsed as shown in the flowchart in FIG. 6. In this case, for example, a state can be assumed in which the fuel tank 41 is filled with the fuel with an ethanol concentration E of 20% when the fuel is fed therein, and the maximum value of the time interval required for the ethanol concentration E of the fuel to change from that immediately after the fuel feed to that equal to or lower than the predetermined concentration Eth can be set to the above-mentioned predetermined period. As a result, unstable engine operation when the engine is restarted can be inhibited.

However, even if the time interval elapsed since the fuel has been fed is the same, the decrease mode of the ethanol concentration E of the fuel differs depending on changes in the engine operation state, changes in the external air temperature, or vehicle running distance. Accordingly, it is desirable that the abovementioned predetermined period be variably set on the basis of changes in at least one of those parameters.

Where the temperature of the fuel stored inside the fuel tank rises following the increase in external air temperature or continuous engine operation, the alcohol with a low boiling point is the first to evaporate. The larger is the amount of alcohol evaporated from the fuel stored in the fuel tank, the lower is the alcohol concentration of the fuel and the higher is the boiling point of the fuel. Further, the longer is the period elapsed since the feed of the fuel into the fuel tank has been performed, the larger is the amount of alcohol evaporated from the fuel stored in the fuel tank.

With the abovementioned configuration, whether or not to drive the cooling fan is determined on the basis of the period elapsed since the feed of the fuel into the fuel tank has been performed. Therefore, the battery power consumption associated with the drive of the cooling fan can be inhibited, while inhibiting the instability of engine operation when the engine is restarted.

Instead of the abovementioned embodiment and the variation example thereof, the ethanol concentration E of the fuel may be determined from the evaporation amount EVA of ethanol in the fuel inside the fuel tank 41 after the feed of the fuel into the fuel tank 41 has been performed, on the basis of changes in at least one of parameters including changes in the engine operation state, changes in the external air temperature, or vehicle running distance, as shown in the flowchart in FIG. 7. Thus, before the evaporation amount EVA of ethanol becomes the predetermined evaporation amount (predetermined evaporation amount EVAth), the cooling fan 55 may be driven after the engine stop, but after the evaporation amount of ethanol becomes equal to or lower than the predetermined evaporation amount EVAth, the drive of the cooling fan 55 after the engine stop may be prohibited.

Where the temperature of the fuel stored in the fuel tank rises following the increase in external air temperature or continuous engine operation, the alcohol with a low boiling point is the first to evaporate. Therefore, the larger is the evaporation of alcohol from the fuel stored in the fuel tank, the lower is the alcohol concentration of the fuel and the higher is the boiling point of the fuel.

With the above-described configuration, whether or not to drive the cooling fan is determined on the basis of the evaporation amount of alcohol in the fuel inside the fuel tank. Therefore, the battery power consumption associated with the drive of the cooling fan can be inhibited, while inhibiting the instability of engine operation when the engine is restarted.

When the ethanol concentration E of the fuel is equal to or lower than the predetermined concentration Eth, the battery power consumption is inhibited by prohibiting the drive of the cooling fan 55 after the engine stop, as in the above-described embodiment. However, the invention is not limited to such a configuration, and when the ethanol concentration E of the fuel is equal to or lower than the predetermined concentration Eth, the drive of the cooling fan 55 may be restricted, for example, by reducing the amount of electricity supplied to the cooling fan 55 with respect to that in the case where the ethanol concentration of the fuel is higher than the predetermined concentration.

In the abovementioned embodiment and the variation example thereof, the ethanol concentration E of the fuel is determined indirectly, but instead a sensor that directly detects the ethanol concentration E of the fuel may be provided and the drive mode of the cooling fan 55 may be set according to the detection results of the sensor. 

1. A cooling fan control apparatus for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, the cooling fan control apparatus comprising: a controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when an evaporation amount of the fuel inside a fuel tank after a supply of the fuel to the fuel tank is performed is less than a predetermined amount, the alcohol concentration of the fuel is taken to be higher than the predetermined concentration, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the evaporation amount of the fuel inside the fuel tank after the supply is performed is equal to or greater than the predetermined amount, the alcohol concentration of the fuel is taken to be equal to or lower than the predetermined concentration.
 2. The cooling fan control apparatus for a radiator according to claim 1, wherein: the predetermined concentration is an alcohol concentration of the fuel when a boiling point of the fuel that changes according to the alcohol concentration of the fuel is at a maximum value attainable by a temperature of the fuel after the internal combustion engine is stopped.
 3. (canceled)
 4. (canceled)
 5. The cooling fan control apparatus for a radiator according to claim 1, wherein: the internal combustion engine is provided with an intake passage for introducing intake air into the internal combustion engine, and an evaporated fuel processing device that introduces an evaporated fuel produced by evaporation of the fuel inside the fuel tank, into the intake passage, the controller that calculates a purge amount integral value which is an integral value of an amount of the evaporated fuel introduced into the intake passage after the supply of the fuel to the fuel tank is performed, that performs the drive of the cooling fan after the internal combustion engine is stopped, when the purge amount integral value is less than a predetermined value, the alcohol concentration of the fuel is taken to be higher than the predetermined concentration, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the purge amount integral value is equal to or higher than the predetermined value, the alcohol concentration of the fuel is taken to be equal to or lower than the predetermined concentration.
 6. The cooling fan control apparatus for a radiator according to claim 1, comprising: an estimation device that estimates an alcohol concentration of the fuel, wherein when the alcohol concentration of the fuel estimated by the estimation device is equal to or lower than the predetermined concentration, the drive of the cooling fan after the internal combustion engine is stopped is restricted.
 7. The cooling fan control apparatus for a radiator according to claim 6, wherein the controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration, regardless of the evaporation amount of the fuel inside the fuel tank after the supply of the fuel to the fuel tank.
 8. A cooling fan control apparatus for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, the cooling fan control apparatus comprising: a controller that performs the drive of the cooling fan after the internal combustion engine is stopped, when an evaporation amount of the alcohol in the fuel inside a fuel tank after a supply of the fuel into the fuel tank is performed is less than a predetermined amount, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, when the evaporation amount of the alcohol after the supply is performed is equal to or greater than the predetermined amount.
 9. A cooling fan control apparatus for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, the cooling fan control apparatus comprising: a controller that performs the drive of the cooling fan after the internal combustion engine is stopped, before a predetermined period elapses from a supply of the fuel to a fuel tank, and that restricts the drive of the cooling fan after the internal combustion engine is stopped, after the predetermined period has elapsed from the supply.
 10. A cooling fan control method for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, comprising: driving the cooling fan after the internal combustion engine is stopped when an alcohol concentration of the fuel is higher than a predetermined concentration; and restricting the drive of the cooling fan after the internal combustion engine is stopped when the alcohol concentration of the fuel is equal to or lower than the predetermined concentration.
 11. A cooling fan control method for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, comprising: driving the cooling fan after the internal combustion engine is stopped when an evaporation amount of the alcohol in the fuel inside a fuel tank after a supply of the fuel into the fuel tank is performed is less than a predetermined amount; and restricting the drive of the cooling fan after the internal combustion engine is stopped when the evaporation amount of the alcohol after the supply is performed is equal to or greater than the predetermined amount.
 12. A cooling fan control method for a radiator that is used in an internal combustion engine capable of using a fuel in which gasoline is mixed with an alcohol with a boiling point lower than that of the gasoline, the cooling fan control apparatus that controls drive of an electric cooling fan provided in the radiator of the internal combustion engine, comprising: performing the drive of the cooling fan after the internal combustion engine is stopped, when an evaporation amount of the fuel inside a fuel tank after a supply of the fuel to the fuel tank is performed is less than a predetermined amount, the alcohol concentration of the fuel is taken to be higher than the predetermined concentration; and restricting the drive of the cooling fan after the internal combustion engine is stopped, when the evaporation amount of the fuel inside the fuel tank after the supply is performed is equal to or greater than the predetermined amount. the alcohol concentration of the fuel is taken to be equal to or lower than the predetermined concentration. 